An angular rate sensor includes a drive-purpose vibrator capable of vibrating along a first direction and an angular velocity detection-purpose vibrator capable of vibrating along a second direction perpendicular to the first direction.
Generally speaking, this sort of angular rate sensor has been constituted by employing a supporting substrate, the drive-purpose vibrator, and the angular velocity detection-purpose vibrator. The drive-purpose vibrator has been supported on this supporting substrate in such a manner that the drive-purpose vibrator can be vibrated along the first direction. The angular velocity detection-purpose vibrator has been supported on the supporting substrate in such a manner that the angular velocity detection-purpose vibrator can be vibrated along the second direction perpendicular to the first direction. This sensor is disclosed in, for example, Japanese Patent No. 2888029.
However, since the angular velocity detection-purpose vibrator has been manufactured in such a shape which is elongated along the second direction, only a very small amount of the vibrations produced from the drive-purpose vibrator is transferred with respect to this angular velocity detection-purpose vibrator. Therefore, there are some possibilities that this angular velocity detection-purpose vibrator may bend along the width direction of the vibrator, i.e., along the first direction.
The angular velocity detection-purpose vibrator outputs the detected angular velocity in accordance with capacitance change produced between the angular velocity detection-purpose vibrator and an angular velocity detection-purpose fixed electrode. However, if the angular velocity detection-purpose vibrator bends, the capacitance change caused by this bending may occur, and thus, angular velocity components other than such an angular velocity component which should be originally detected are detected. As a result, the unwanted angular velocity components may cause a detection output error.
When the angular velocity detection-purpose vibrator bends along the first direction, this angular velocity detection-purpose vibrator is deformed also along the second direction in connection with the first direction. As a result, the distance (interval) between the angular velocity detection-purpose vibrator and the angular velocity detection-purpose fixed electrode along the second direction is changed. Thus, the capacitance change is produced based upon this distance change.
Thus, it is required to protect the angular velocity detection-purpose vibrator from bending due to driving vibrations of the drive-purpose vibrator, and further, it is required to reduce a detection output error.
Further, a mounting structure of an angular rate sensor in which a vibration type angular rate sensor is mounted on a base member. In the vibration type angular rate sensor, while a vibrator is driven to be vibrated, when an angular velocity is applied to this angular rate sensor, the applied angular velocity is detected based upon vibrations of the vibrator along a direction perpendicular to the driving vibration direction.
In general, as this sort of vibration type angular rate sensor, MEMS (Micro Electro Mechanical System) gyroscopes have been known.
Such a vibration type angular rate sensor has been arranged by employing: a base unit made of a semiconductor substrate, or the like; a vibrator coupled to the base unit; excitation means for driving the vibrator to be vibrated along a first direction; and detection means for detecting an angular velocity. That is, when the angular velocity is applied under driving vibrations of the vibrator, this detection means detects the applied angular velocity based upon the vibrations of the vibrator along a second direction perpendicular to the first direction.
Such a vibration type angular rate sensor is employed as a yaw rate sensor for detecting a yaw rate in a system such as, for instance, a Vehicle Stability Control (VSC) and a navigation system. This vibration type angular rate sensor is mounted on a vehicle under such a condition that this yaw rate sensor is mounted on, for example, a mounting board of an Electronic Control Unit (ECU) as a base member.
In this case, an angular rate sensor is mounted in such a way that a detection axis corresponding to a rotation axis of an angular velocity is directed to an upper and lower direction of a vehicle, namely the vertical direction.
However, in such a case that this angular rate sensor is used so as to detect any other angular velocities than a yaw rate, the sensor is mounted in such a manner that a detection axis of an angular velocity is located parallel to a horizontal plane. The angular velocities other than this yaw rate correspond to, for instance, an angular velocity around an axis of a forward and backward direction of a vehicle, namely a roll rate, and also correspond to an angular velocity around an axis of a right and left direction of the vehicle, namely a pitch rate.
As a result, in the angular rate sensor, there are some risks that adverse influences caused by the upper and lower vibrations of the vehicle and the gravitational acceleration may be given with respect to the driving vibrations depending upon the direction of the driving vibrations of the vibrators. In other words, when the above-described upper and lower vibrations of the vehicle and the gravitational acceleration are applied to the vibrators along the above vibration direction, the vibrating conditions of the driving vibrations become unequal to each other.
Originally, in a vibration type angular rate sensor, it is important how to stabilize driving vibrations of vibrators. However, a leakage of vibrations may occur in response to a change in conditions of the driving vibrations, and/or electric anomalies, caused by the driving vibrations being superimposed upon detection signals, so that precision of sensor output signals may be deteriorated.
Therefore, it is required, even when a detection axis of an angular velocity is directed to the horizontal plane, driving vibrations of vibrators is stabilized as much as possible.